1. Technical Field
The invention relates to a rotary table or ring, and, more particularly, to a method and apparatus utilizing such rotary table or ring for transferring and positioning manufacturing workpieces.
2. Description of the Problem
Rotary transfer machines are advantageously applied to positioning articles for machining, assembly and/or processing where multiple operations are necessary for completion. An exemplary use of rotary transfer machines is to machine close tolerances into die cast workpieces. Rotary transfer machines typically rotate and index workpieces from station to station via a rotary index table (sometimes referred to as a “Lazy Susan”) mounted in the center of the stations. A drive control, typically a geneva drive mechanism or a two face gear coupling, performs intermittent indexing and rotating of the index table to cycle the workpieces sequentially through the stations.
Obtaining access to multiple surfaces of an article or workpiece undergoing processing is an advantage of rotary index tables, though there have been limitations even here. The rotary index table typically has mounted thereon several clamping pallets that hold workpieces in position. The machine tools may drive a spindle radially inward into the workpiece towards the center of the table, or may work vertically above the workpiece, or may work at an angle therebetween. The clamping pallets may either be fixed relative to the rotary index table or capable of being rotated, tilted or otherwise moved relative to the rotary index table by mounting the pallets on satellite tables that are rotatable relative to the index table. By rotating the satellite table, more sides of the workpiece are exposed to allow for machining of more sides of the workpiece. It is much less desirable to move or rotate the workpiece relative to the index table once it is locked into position for a variety of reasons. One reason is that doing so decreases the tolerances between different machining operations performed at different stations because there are two different axes of rotation which allows for play between rotational axes. Another reason is that cycle time is increased which results in an inefficiency reducing the production rate of the rotary transfer machine. Yet another reason is the high cost associated with providing the satellite tables and appropriate drive and positioning means for selectively positioning each of the satellite tables.
Thus rotary index tables have found limited success, particularly in use of manufacturing stations or cells. One drawback to the use of such rotary index tables, is the necessity of having the processing or work stations about the outer periphery of table which causes the workstations to be directed radially inward toward the center of the table. This geometry creates problems in work stations access and visibility during tooling setup, production, and maintenance procedures.
Tolerance problems regarding starting, stopping, locking, and combined rotation of the table limit usefulness of the rotary table in some applications. Controllability of the rotation of the table has been previously accomplished with rotational gear type drives or expensive digital servomotors and the like. Further, precision in flatness and location of rotary table during use has, in the past, been insufficient.
In view of the foregoing, there is a need for a rotary table that provides improved access to the workpiece and eliminates undesirable movement introduced by conventional drive mechanisms, and introduces exact and highly stable positioning, without sacrificing the benefits of inexpensive construction and precision in rotation and flatness.